1. Field of the Invention
The present invention relates to pickup units of electric stringed instruments, which pick up vibrations of strings and convert them into electric signals.
The present application claims priority on Japanese Patent Application No. 2009-133812 (Filing Date: Jun. 3, 2009), the content of which is incorporated herein by reference.
2. Description of the Related Art
Conventionally, electric stringed instruments such as electric guitars and acoustic guitars have been equipped with pickup units that pick up vibrations of saddles supporting strings so as to generate electric signals. Conventionally-known examples of pickup units of electric stringed instruments are disclosed in Patent Documents 1 and 2, as follows:                Patent Document 1: Japanese Patent Application Publication No. H07-239684        Patent Document 2: Japanese Patent Application Publication No. H07-239685        
FIGS. 5A and 5B show the conventionally-known constitution of a pickup unit 50 adapted to an electric stringed instrument. The pickup unit 50 is fixed inside a recess 52A of a lower bridge 52 attached to an exterior board 51 of an electric stringed instrument. The pickup unit 50 is constituted of a U-shaped frame 55 (having a U-shape in side view, see FIG. 5B) installed in the recess 52A, a vibrator 57 which is inserted and held by the U-shape frame 55 and of which upper end supports strings 56, a plurality of piezoelectric elements 58 which are interposed between the U-shape frame 55 and the vibrator 57 and which are disposed just below the strings 56 respectively, and a shim 59 interposed between the bottom portion of the recess 52A and the U-shape frame 55.
The vibrator 57 is constituted of a saddle 60 made of a resin, and a lead plate 61 which is fixed to the lower surface of the saddle 60 and which conducts with the upper surface of the piezoelectric elements 58. Owing to the downward force exerted by the strings 56 which are stretched under tension, the piezoelectric elements 58 are brought into contact with the lead plate 61. Upon playing an electric stringed instrument, vibrations of the strings 56 are transmitted to the vibrator 57 (supporting the strings 56) toward the piezoelectric elements 58, which are thus deformed in shape to generate electricity. Thus, it is possible to convert vibrations of the stings 56 into electric signals. In the preparation of an electric stringed instrument, manual operation is needed to adjust the heights of the strings 56 and to adjust the projecting length of the saddle 60 above the lower bridge 52. This manual operation is performed using a plurality of shims 59 having different thicknesses, wherein each of the shims 59 is arbitrarily selected and applied to the pickup unit 50, thus performing the above mechanical adjustment.
The pickup unit 50 shown in FIGS. 5A and 5B is characterized in that the downward force of the strings 56 may fluctuate during the performance of an electric stringed instrument, and the saddle 60 may be inclined toward the neck of an electric stringed instrument so as to loosen the tight contact between the piezoelectric elements 58 and the lead plate 61 when the strings 56 are being stretched. This destabilizes the contact state between the piezoelectric elements 58 and the lead plate 61, so that the piezoelectric elements 58 may not deform to readily follow up with vibrations of the saddle 60. That is, the pickup unit 50 suffers from a great mechanical loss in transmitting vibrations to the piezoelectric elements 58, a destabilization of vibrations of the strings 56, and a difficulty in precisely converting vibrations of the strings 56 into electric signals.
In addition, the pickup unit 50 suffers from a difficulty in maintaining the uniform contact state between the piezoelectric elements 58 and the lead plate 61, which in turn readily causes dispersions regarding the tone volume of the strings 56. The piezoelectric elements 58 inherently possess an inclination to greatly fluctuate in electric power generation depending upon a subtle difference of the contact state with the lead plate 61, thus easily revealing the above drawbacks. The saddle 60 of which base portion has a low precision of smoothness may induce a great fluctuation of electric power generation among the piezoelectric elements 58, which in turn causes dispersions regarding the tone volume of the strings 56. For this reason, a further process is needed to improve the precision of smoothness after the formation of the saddle 60 made of a thermosetting resin.
The pickup unit 50 of FIGS. 5A and 5B is simply assembled such that the piezoelectric elements 58, the lead plate 61, and the saddle 60 are sequentially mounted in the recess 52A of the lower bridge 52 on the exterior surface 51 of an electric stringed instrument. For this reason, even when the surface of the lead plate 61 is smoothed, it is difficult to practically secure the same contact state among the piezoelectric elements 58 with the lead plate 61. Since the contact pressure of the piezoelectric elements 58 normally fluctuates owing to vibrations of the strings 56, the piezoelectric elements 58 partially contacts with the lead plate 61 with respect to micro-time. This degrades the sound quality and tone color of an electric stringed instrument. Since the tone color of an electric stringed instrument is inherently correlated to the initial plucking period, fluctuations of contact pressure greatly affect the tone color of an electric stringed instrument as they are apt to increase in the initial plucking period.
Furthermore, the shim 59 disposed in the bottom portion of the recess 52A of the lower bridge 52 causes a mechanical loss in transmitting vibrations to the lower bridge 52 and the body of an electric stringed instrument. For this reason, it is difficult to reproduce a live sound of an electric stringed instrument with the conventionally-known constitution of the pickup unit 50.